Effects of H+ and OH− on H2O as probed by the 1-propanol probing methodology: differential thermodynamic approach

Abstract

We applied what we call the “1-propanol (1P) probing methodology” on the effects of H⁺ and OH⁻ on liquid H₂O. We found that H⁺ is an amphiphile with a modest hydrophobic and an equally modest hydrophilic contribution. Its hydration number is 2 ± 1, suggesting that the equilibrium hydration structure is like the Zundel type (H₅O₂⁺). OH⁻, on the other hand, has a large hydration shell with 12 ± 3 H₂O molecules and acts as a hydrophobe-like hydration center. In other words, it forms a hydration shell around itself, but as the probing 1P increases and the available H₂O decreases, it exerts its influence over a longer range and reduces the hydrogen-bond probability of bulk H₂O away from hydration shells, just as a hydrophobe does to bulk H₂O.